High Performance iOS Networking, v1.20

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High Performance iOS Networking, v1.2.0 @smithclay / New Relic iOSDevUK September 2016

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- MENU - ■APPS TODAY LATENCY WOES PROTOCOLING MORE PROTOCOLING DEBUGGING

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The Client Server A E S T H E T I C data Server Client Newton Image CC 2.0 SA, flickr.com/photos/moparx/5321857668 data

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Apps Today Client Newton Image CC 2.0 SA, flickr.com/photos/moparx/5321857668 Analytics Auth Ads Custom Content CDN API Gateway

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DANGER Network latency ahead Newton Image CC 2.0 SA, flickr.com/photos/moparx/5321857668

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-Physics! "Information can't travel faster than the speed of light."

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• Wales to San Francisco: 5,284 mi (8503km) • Speed of Light in Fiber Optic Cable: 2*10^8 m/s • Human "this wasn't instantaneous" time: 100ms • We can perceive global network latency even under perfect conditions: YES

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Protocols So what's the deal with...

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Full TCP Handshake 1. SYN 2. SYN/ACK 3. ACK Data { Round trip { Client/Device Server RTT Count: 2

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Full TCP + TLS Handshake Client/Device Server Data Transfer { Round trip 1. SYN 2. SYN/ACK 3. ACK { { TLS, +2 RTTs RTT Count:+2 Required for ATS!

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TCP Fast Open (TFO) Client/Device Server 1. SYN 2. SYN/ACK+cookie 3. ACK Data { Round trip { http://devstreaming.apple.com/videos/wwdc/2015/719ui2k57m/719/719_your_app_and_next_generation_networks.pdf?dl=1 RTT Count: 2

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TFO,#2 Req Client/Device Server 1. SYN+cookie 2. SYN/ACK+data { Round trip iOS 9+ supports this, but you're probably not going to use the low-level APIs to make this work. RTT Count:1

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Protocol Performance Tips for App Devs Generally: reduce connections Use latest TLS version $ nscurl --ats-diagnostics Physically closer is better Don't tune (unless you have to)* *If you are going to: https://tools.ietf.org/html/draft-stenberg-httpbis- tcp-01 + https://istlsfastyet.com

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HTTP/2 So what's the deal with...

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iOS 9+ w/ NSURLSession

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H2 Connection Multiplexing Client/Device Server Over a single TCP connection, multiple HTTP messages can be sent more efficiently. Connection closes Connection opens

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H2 ADVANCED FEATURES HEADER COMPRESSION STREAM PRIORITIES (iOS 10) SERVER PUSH (iOS 10)

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• Likely will need to upgrade your HTTP server... • Major Content Delivery Networks (CDNs) support it. • https://tools.keycdn.com/http2-test • https://blog.newrelic.com/2016/02/17/http2- production/ Server-side support

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HTTP/2 Tips for iOS Devs H2 is not magic perf sauce Server-side push not well understood (yet)* Having metrics in place before switch is critical * Google is helping with this: https://docs.google.com/document/d/1K0NykTXBbbbTlv60t5MyJvXjqKGsCVNYHyLEXIxYMv0/edit Supported in NSURLSession

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Caching So what's the deal with...

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-Common Sense/Unknown "The fastest network request is one you don't have to make."

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• NSURLRequestUseProtocolCachePolicy (default policy for NSURLSession) observes the protocol spec. • Cache-Control: max-age=, public Cache-Control Header

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ETag Header Client/Device Server ETag headers can inform clients they already have the requested resource. 200 OK Last-Modified: Mon, 22 ETag: ad87... GET /fave-cats.json GET /fave-cats.json If-None-Matched: ad87.. 304 Not Modified

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Enabling more rapid server-side change "Backends for frontends" (BFFs) See: Netflix, Spotify (and others) Device "iOS Client Service" Ye Olde Systems HTTP2/ gRPC (?) QUIC (?) HTTP 1.1/ Terrible XML Stuff

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• API Versioning (using headers—backwards compatible) • Horizontally scalable • Gateway for other legacy systems • Downside: must be highly available BFF attributes

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Debugging So what's the deal with...

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CF_NETWORK Diagnostics https://developer.apple.com/library/ios/qa/qa1887/_index.html

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Example log

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Remote Virtual Interface • rvictl creates an interface for packet capture tools (i.e. wireshark) • Device must be plugged in using USB • https://developer.apple.com/ library/mac/qa/qa1176/ _index.html • useyourloaf.com/blog/remote- packet-capture-for-ios-devices/

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Wireshark Setup Download: http://wireshark.com/

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Total Packet V I S I B I L I T Y

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Instruments: Network

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Not my go-to (sorry)

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HTTP Proxies • mitmproxy: mitmproxy.org (0.16 supports HTTP/2!) • charlesproxy.com/Fiddler (Nice UI, paid, no HTTP/2 support yet) • Will not work with certificate pinning (no MITM permitted)

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1. El Capitan python issues: use brew install python 2. For simulator, must set proxy on OS X to 127.0.0.1:8080 to start capturing HTTP(S) traffic. 3. Must install certificate after running proxy: go to http://mitm.it on simulator. mitmproxy install notes

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Example http://docs.mitmproxy.org/en/latest/mitmproxy.html

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NSURLSession Metrics [new!] New in iOS 10! Thanks Apple! func urlSession( _ session: NSURLSession, task: NSURLSessionTask, didFinishCollecting metrics: NSURLSessionTaskMetrics) • Number of Redirects, time it took task to complete • Whole lot of goodness in NSURLSessionTaskMetrics • Build your own waterfall! • https://developer.apple.com/reference/foundation/ nsurlsessiontasktransactionmetrics

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Thoughts Use NSURLSession. Audit server-side: using latest TLS? Is caching configured correctly? HTTP2? Consider using a CDN and measure latency! Reduce number of requests per host. Read https://hpbn.co/